Optical lens.



V Drafismam PATENTED FEB. 25, 1908. J. B. GERMAIN & G. A. OSSART.OPTICAL LENS.

APPLICATION FILED MAR. B, 1907.

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UNITED- STATES PATENT oF Ic JULES- EUGENE GERMAIN' AiNlJ GEORGES ARSENEQSSART, OF RUEIL, FRANCE, ASSIGNORSI TO JULES ALPHONSE GUSTAVE ROUSSET,OF VINCE-REES,

OPTICAL S.

Specification of Letters Patent.

Patented Feb. 25,1,eqe.

Application filed March 8. 1907- Sarial No. 361.403.

T 0 all whom it may concern:

Be it known that we, J ULES EUGENE GER- MAIN and GEORGES ARsENE OSSART,citizens of the Republic of France, residing at Rueil, in said Republic,have invented certain new and useful Improvements in Optical Lenses, ofwhich the following is a specification.

This invention aims to provide an optical lens which is applicable tovarious purposes and characterized by practically perfect aplanatism andachromatism.

It is a further object of the invention to provide a lens in which theimage of the different planes, from those situated quite close to thelens to those infinitely distant, is produced sharply and in one and thesame focal plane without using a diaphragm.

In the accompanying drawing, in which the same reference charactersdenote the same parts throughout the views, Figure 1 illustratesdiagrammatically the form of the lens as compared to an ordinaryspherical lens, Fig. 2 shows a device for tracing the meridian curve ofthe lens, and Figs. 35 show curves generated by said device and afterwhich lenses are shaped according to this invention.

The considerations upon which the formation of a lens of this kind arebased are as follows: Assuming a plano convex spherical lens, theintersection of which by the plane of the figure is b a c (Fig. l) andthat d ais the radius of the arc of a circle I) a c. Assuming also aluminous point e and e a as the ray emanating from the point e passingthrough the optical center. The image of the point e should-be formed ate on.the pro longation of the ray e a on encountering all the otherluminous rays issuing from the point e and refracted by the lens. It isknown however that this point of encounter is not a single point, therays falling near the edge 0 of the lens intersecting the prolongationof the ray e a much nearer the lens than those falling near the center.It is therefore necessary to cause the position of the point e to vary,or by causing it to vary very slightly to make the points such as f andg to coincide with the point e. In accordance with the invention, thisresult is obtained by modifying the form of the exit surface of thelens, in such a manner that the meridian of this surface which from thesummit a to the point it almost coincides progressively, while beingexternal to it from h to i. In these conditions the rays emanating fromthe point c after their refraction in the lens meet at one and the samepoint e.

If in place of a lano-convex lens a convergent bi-convex meniscus beconsidered, it will be understood that the modification of the luminousrays on leaving the lens may be obtained in two ways; either as juststated, by modifying the discharge surface, or by modifying theadmission surface in order to modify, by this very fact, the directionin the interior of the lens of the refracted rays and consequently thedirection of the rays leaving the lens. These two methods may however becombined; finally the meridian deformation curves may be internal to themeridian circle of the spherical lens in question, if it is desired todlminish the distances of the focal plane. Startin from theseconsiderations, it was first of a l necessary to provide an apparatuspermitting of tracing in a continuous manner in a plane, the deformationcurves for replacing the meridian circle of a sphericallens. Thisapparatus .as shown in Fig. 2 consists broadly of a bar 3' capable ofsliding and turning around "a fixed pivot one extremity 7' provided witha nut being traversed by a'screwk. At the other extremity of the bar 1'there is fixed a pencil 3". When the screw is is turned, the bar 7'slides over the pivot j and at the same time turns about it, and thepencil describes a curve such as the curve I represented in Fi 3.

By modifying the position of the pivot y" relatively to the extremity jof the bar, curves are obtained like the curve II (Fig. 3) eitherinternal or external to the circle taken as base. Concentric curves maybe obtained by displacing the pencil 9" and the position of the fixedpivot 7" simultaneously by the same amount; the curve IV concentric withthe curve I is obtained in this manner. In the same way the pencil maybe placed between the extremity j' of the bar and the fixed pivot j; thecurve described is then analogous to that indicated at III, Fig. 3. Thepencil may also be placed at the prolonged extremity j of the bar.Instead of the extremity j of the bar describing a straight line, it maybe compelled to describe a circle. In this case the screw is replaced bya disk. The curves obtained are analocertain amount and by decreasingthe radius gous to the preceding curves. Fig. 4 shows] the curve Vdescribed by starting from the circle VI as base. Concentric curves areobtained, Fig. 5, by moving the pencil up by a of the circle describedby the extremity of the bar opposite to the pencil, by the same amount.If without changing the radius of this circle the fixed pivot is movedtowards the pencil increasingly pointed curves are drawn; by displacingthe pivot in the opposite direction increasingly elongated curves areobtained. It is therefore possible to draw deformation curves having thesame summit and different curvatures, but in as close proximity asdesired.

In order to form-a lens, the summits of the curves such as those shownin Fig. 5 are combined. For example, if it is desired to form aconvergent meniscus, the summits Zm n 0 internal on the side of theimage are combined with the summits Z m n 0" which will form theexterior curves turned towards the object. It is also possible tocombine the curves Z m n 0 or to combine the curves Z m n 0. The choiceof these combinations will be determined by the important fact thatinorder to obtain a good combination it is essential that the lenstested as a magnifying glass should give a magnification equal from thecenter to the edge.

The curve generated by the device described and which forms the meridiancurve of the lens is a conchoid. When the extremity describes a straightline the curve generated is a conchoid of a line or a lineal conchoid;its equation, of the fourth degree,

enters and that through which it leaves which form the interior curvesis (w +y (wa) =Z w When said eX- tremity describes a circle the curvegenersec 20s ated is a conchoid of a circle; its equation,

of the sixth degree, is (90 +y (w +y a R Z 4R (m g can) la y KH Z Thusthe meridian curve of the lens is not formed by deforming a sphere, butis generated and defined geometrically; one can construct the normal ateach point by geometry, and it is possible with this meridian to followgeometrically the rays of light.

Both the face through which the light the lens are conchoidal. Thelenses may be I formed automatically by a machine in which provision ismade for an infinite number of variations in the form given to theconchoidsQ In this manner the shaping of the lens point by point by amethod analogous to that of Foucault, or by means of templets, as .isnecessary when the form of the lens isobtained by calculation, isavoided.

Having thus described our invention, we claim: V

1. An optical lens having a meridian curve which is a true conchoid.

2. An optical lens having the -meridian curves of its admission and itsexit surfaces conchoidal in form.

3. An optical lens having as its meridian curve a fourth degree curve ofthe following equation: (x 3 (a: (1) Fr? In testimony whereof we havesigned this specification in the presence of two subscribing witnesses.

JULES EUGENE GERMAIN. GEORGES ARSENE OSSART.

Witnesses:

EMILE LEDRET, DEAN B. MAsoN.

